1. Field of the Invention
The present invention relates to an image processor for printing used in an electronic printer provided with a print engine, particularly relates to an image processor for printing wherein compressed image data every color in predetermined color space is supplied, is expanded and is supplied to a print engine.
The present application is based on Japanese Patent Application No. Hei. 11-95078, which is incorporated herein by reference.
2. Description of the Related Art
An electronic printer such as a page printer prints image data in predetermined color space generated by a host computer and others by a print engine utilizing a laser beam and others. Such an electronic printer generates image data corresponding to plural colors in color space corresponding to the colors of toner, forms a latent image on a drum according to image data of each color in the print engine, fixes toner of the corresponding color and transfers it on printing paper. Therefore, such an electronic printer is provided with an image memory (or a band memory) for storing image data for at least one page and further, an image processor for processing image data stored in the image memory and generating image data adapted to the print engine.
Normally, as the quantity of image data stored in an image data is enormous, it is stored in the image memory as image data compressed according to a predetermined algorithm. Therefore, the image processor at least expands such compressed image data and supplies the expanded image data to the print engine.
A conventional type image processor expands compressed image data every color and supplies it to a print engine as it is. Therefore, the image processor starts the expansion of compressed image data and supplies the expanded image data to the print engine according to a horizontal synchronizing signal corresponding to the printing timing of the print engine or a video clock (or a dot clock). If compressed image data is expanded, the image data of the preceding raster is required to be referred depending upon algorithm for compression and in that case, the image processor instructs to once store the expanded image data and refers to the preceding expanded image data with the start of expansion.
As described above, the conventional type image processor is required to execute all image processing such as internal expansion processing and the reference of the preceding expanded image data for expansion depending upon the printing timing of the print engine.
An electronic printer may also receive the image data of RGB from a host computer and may also receive the image data of CMYK corresponding to toner of a print engine. An image processor in a conventional type electronic printer processes only the image data of CMYK corresponding to toner utilized in a print engine. Therefore, when the image data of RGB is supplied, it is converted to the image data of CMYK by a color conversion unit in an electronic printer and the compressed image data of CMYK for one page for example is stored in an image buffer (a band memory). When the image data of CMYK is supplied, it is compressed as it is and is stored in an image buffer. Afterward, as described above, the above image data is expanded by the image processor in accordance with the timing of the print engine and is supplied to the print engine.
However, fixed processing time is required to convert the image data of RGB for one page and in a method of once compressing the converted image data of CMYK, storing it in the image buffer and afterward expanding it every raster, a long time is required for printing. Particularly, color conversion processing is equivalent to overhead in printing processing and it takes a long time until printing is started.